Datasheet

SCAN921025H, SCAN921226H
www.ti.com SNLS185C –OCTOBER 2004–REVISED MAY 2013
APPLICATION INFORMATION
USING THE SCAN921025H AND SCAN921226H
The Serializer and Deserializer chipset is an easy to use transmitter and receiver pair that sends 10 bits of
parallel LVTTL data over a serial Bus LVDS link up to 800 Mbps. An on-board PLL serializes the input data and
embeds two clock bits within the data stream. The Deserializer uses a separate reference clock (REFCLK) and
an onboard PLL to extract the clock information from the incoming data stream and then deserialize the data.
The Deserializer monitors the incoming clock information, determines lock status, and asserts the LOCK output
high when loss of lock occurs.
POWER CONSIDERATIONS
An all CMOS design of the Serializer and Deserializer makes them inherently low power devices. In addition, the
constant current source nature of the Bus LVDS outputs minimizes the slope of the speed vs. I
CC
curve of
conventional CMOS designs.
POWERING UP THE DESERIALIZER
The SCAN921226H can be powered up at any time by following the proper sequence. The REFCLK input can be
running before the Deserializer powers up, and it must be running in order for the Deserializer to lock to incoming
data. The Deserializer outputs will remain in tri-state until the Deserializer detects data transmission at its inputs
and locks to the incoming data stream.
TRANSMITTING DATA
Once you power up the Serializer and Deserializer, they must be phase locked to each other to transmit data.
Phase locking occurs when the Deserializer locks to incoming data or when the Serializer sends patterns. The
Serializer sends SYNC patterns whenever the SYNC1 or SYNC2 inputs are high. The LOCK output of the
Deserializer remains high until it has locked to the incoming data stream. Connecting the LOCK output of the
Deserializer to one of the SYNC inputs of the Serializer will ensure that enough SYNC patterns are sent to
achieve Deserializer lock.
The Deserializer can also lock to incoming data by simply powering up the device and allowing the “random lock”
circuitry to find and lock to the data stream.
While the Deserializer LOCK output is low, data at the Deserializer outputs (ROUT0-9) is valid, except for the
specific case of loss of lock during transmission which is further discussed in the RECOVERING FROM LOCK
LOSS section below.
NOISE MARGIN
The Deserializer noise margin is the amount of input jitter (phase noise) that the Deserializer can tolerate and still
reliably receive data. Various environmental and systematic factors include:
Serializer: TCLK jitter, V
CC
noise (noise bandwidth and out-of-band noise)
Media: ISI, Large V
CM
shifts
Deserializer: V
CC
noise
RECOVERING FROM LOCK LOSS
In the case where the Deserializer loses lock during data transmission, up to 3 cycles of data that were
previously received can be invalid. This is due to the delay in the lock detection circuit. The lock detect circuit
requires that invalid clock information be received 4 times in a row to indicate loss of lock. Since clock
information has been lost, it is possible that data was also lost during these cycles. Therefore, after the
Deserializer relocks to the incoming data stream and the Deserializer LOCK pin goes low, at least three previous
data cycles should be suspect for bit errors.
The Deserializer can relock to the incoming data stream by making the Serializer resend SYNC patterns, as
described above, or by random locking, which can take more time, depending on the data patterns being
received.
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Product Folder Links: SCAN921025H SCAN921226H